ernal-september.org> 60f0bb88
XPost: comp.lang.pl1, comp.lang.pascal.borland, comp.lang.pascal.misc
From: peter_flass@nospicedham.yahoo.com
Robert Prins wrote:
> Hi all,
>
> Not really specific x86, Virtual Pascal, or PL/I, but as I've got the same
code
> written in all three languages, I'll give it a try here:
>
> I have an array (actually three, but that's not very relevant for the issue)
of
> pointers to items in a linked list. The array is sorted into a specific
order,
> and after the sort, I use it to print Top-N tables. For the main Top-50
table (x
> 3) that's easy enough, the first 50 items are selected.
>
> However, at this time the linked list also contains 5 sub-lists, each
containing
> additional sub-lists for a total of 390 (yes, three-hunderd-and-ninety)
> sub-lists for which I want to print Top-10 tables (or if a sub-list contains
> just 4 items, a Top-4 table). Because I don't really want to sort the main
array
> six (x 3) times, I just scan the array from the top, and pick out the items
for
> each sub-list, until I have 10 (or the 4 mentioned before) items. To speed up
> the process a little, I make an initial pass over the array to find the first
> item for each sub-list, but that doesn't really improve things a great deal.
>
> So given that "this" is the list, sorted on its main key, with the second and
> third columns identifying additional sub-lists,
>
> 100, 'a', '1'
> 099, 'b', '9'
> 098, 'c', '1'
> 097, 'b', '8'
> 096, 'd', '3'
> 095, 'a', '2'
> 094, 'c', '8'
> 093, 'c', '1'
> 092, 'a', '3'
> 091, 'f', '4'
> 090, 'a', '2'
>
> the "Top-50" would contain the above.
>
> For sub-list 'a', I would scan the array, and the resulting "Top-10" would be
>
> 100, 'a', '1'
> 095, 'a', '2'
> 092, 'a', '3'
> 090, 'a', '2'
>
> Likewise, for sub-list 'b', I would scan the array, and the resulting
"Top-10"
> would be, and the initial fill-the-cache scan would have set the starting
index
> for the 'b' sub-list to the cell containing 099, saving me one superfluous
compare.
>
> 099, 'b', '9'
> 097, 'b', '8'
>
> etc, and the same would happen for the sub-lists defined by column 3, the
first
> being
>
> 100, 'a', '1'
> 098, 'c', '1'
> 093, 'c', '1'
>
> As I wrote, I make an initial pass over the data to cache the first item for
> each sub-list, some of them consist of a single item and are nearly at the
end
> of the sorted full array, and this saves some time, the count of executed
> statements is reduced by around 10%, but if anyone can think of a way to
speed
> up things a bit more, without having to sort the array(s) five more times
(in an
> additional 10,000,000 executed statements, see below), please share it with
me.
>
> Some numbers:
>
> - the caching code executes around 120,000 PL/I statements
> - sorting the three arrays executes around in 2,000,000 PL/I statements
(using a
> Heapsort)
> - printing the 390 top-n tables executes around 7,600,000 PL/I statements,
and
> the "IF" statement that selects the data to be printed has a hit-percentage
of
> just 0.5%:
>
> IF STY_TCN = 'Tr' & STY = LIST.TR | /* 208 type 1 */ 1,841,754 executed IF's
> STY_TCN = 'Na' & TCN = LIST.NA | /* 93 type 2 */
> STY_TCN = 'Yr' & STY = LIST.YR | /* 37 type 3 */
> STY_TCN = 'Co' & TCN = LIST.CO | /* 33 type 4 */
> STY_TCN = 'Ty' & TCN = LIST.TY | /* 19 type 5 */
> STY_TCN = '**' THEN /* 1 main */
> DO;
> #T = #T + 1; 9,594 - the actual
> number of Top-N lines printed
>
> Robert
Assuming mainframe, the rule-of-thumb I learned was "let the sort do the
work" since DFSORT is always more efficient than any user code. I can't
visualize what you're doing from your description, but if possible I'd make
one pass of the data and build records that can be sorted into the desired
sequence by DFSORT. Then read the sorted records and print the listings. I
would use PLISRTD to build and retrieve the records, but some would
probably prefer two separate programs with the sort in between invoked by
JCL, or build the records and ATTACH the sort, or...
--
Pete
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
|
